Well, I broke down and bought the service notes. I'll get it scanned and posted here in the coming weeks, but it's an ugly, many-foldouts kind of thing. To answer my original question, there aren't really any easy cool tricks to be played. Yeah, you can bring out the filter and resonance pots, but as far as easy tricks go, there's only one other good one:

The presets are not digital momentary pushbutton switches. Behind those buttons are a series of resistors… sorta like a CV keyboard. That feeds into ADC, which chooses the preset based on the input voltage (0-4v). 4 volts means "synth 2." 2.5 volts means "flute." So you could hook up an LFO and cycle through presets while you play. Which would be pretty sweet. Maybe.

I've seen the unit described as a preset-only Juno 106, which is wholly inaccurate. For the eight voices, there is one IR3109 (Jupiter, Juno 60) based filter. On the effects side, there are two chorus (mn3009 256 stage BBDs) and vibrato units driven by inverted control voltages to provide stereo effects. There is a global analog VCA, but it's used as an attenuator to compensate for different volumes of the presets.

But where it really departs from the mid-80s Roland mold is the voice architecture. It was my hope to be able to extract the voices independently and get a boring but effective midi-controlled eight-DCO unit to patch into a modular system. No such luck!

The voices are that unhappy kind of digital -- all eight polyphonic voices are internally mixed and come out of the same pin on the tone generator IC (MSM5232RS). All square waves, all the time. Interestingly, analog ADSR envelopes for all eight voices are pumped into the tone generator. These voltages are actually generated by the CPU (PD710G/PD711G) digitally, sent to a R2R DAC and then the _analog_ control is shifted down to +/- 4V and fed into the tone generator.

So the amplitude envelopes for the voices can be controlled externally, but it would be a lot of work. The analog side would be easy, but you'd need a separate module to extract 8 voice gate data from your midi messages using the same voice assignment method as the EM-101. To which I say "meh."

But back to the interesting stuff: Since there's only one filter (and that means no effective keyboard tracking on a polyphonic synth), some of the different timbral characteristics of the sounds are generated by mixing four foot lengths (16', 8', 4' and 2') of square waves together. While all the voices come out premixed, all four footlength stops (16', 8', 4' and 2') are available at the same time (pins 28-31).

But wait, it gets better: All four footlength stops are ALSO available on pins 33-36. These two sets of stops are pumped into two different mixers at different values. The first is mixed with higher harmonics diminishing in amplitude, so that the result is more of a sawtooth-type staircase wave. The second is mixed with all the stops at the same amplitude. This mix is only used for the organ sounds. These mixes are referred to as "waveform a" and "waveform b," and are selected by a 4016. You could put that under external control but I don't think it'd be very exciting.

The catch is that the mixer uses fixed resistors, and not all the voices use all the stops. For voices that do not use all the stops, the unused stops are gated internally to the voice chip. That is, based on what the CPU says, it doesn't output that voice and the relevant pin remains silent. Voices that DO output all the stops include strings 1, strings 2, brass 1, brass 2, bass 1, bass 2, cello, flute, and synth 1.

Let's double back here for a second though. You have two identical sets of four waveforms coming out at the same time. To me, that's potential. Throw those eight guys into a stack of VCA controlled by your favorite modulation sources. LFOs and stuttery gates. Pan the outputs around and you have the potential for a very interesting soundscape.

So man, I'm not sure what I'm going to do with mine. Personally, I think the stock sounds suck. Tearing out the analog board (VCF, VCA, Effects) and just using that for something seems straightforward, but most of the mods that would allow you to leverage the actual voices seem both pain-in-the-assy and would require a crap load of external circuitry to be useful.

Okay. Hope some other EM-101 owner or potential owner gets something out of this.

wow, congratulations for posting the most comprehensive em-101 info on the internet!

I, too, have just acquired one of these, and am still not sure what to do with it.

curious to know if you've done anything in the ~1 mo since your original post? I wonder if the filter/res pots sound any decent once made more tweakable. I like some of the pads ok and the shitty bass actually sounds kinda cool in the lower octaves.

for anyone else who is looking, here's some info I've googled:

- holding "-" and "brilliance" on power on brings up 8 "hidden" presets.

- the tone gen IC is similar/same as MSM5232, which was used in korg poly800 (and similar) synths, as well as some arcade games in the '80s

I can post some service manual pdfs from those synths re: that IC, but sounds like it'd be redundant information..

also! I tracked down someone who has modded this exact unit, he had this to say:

Quote:

Once you have the service manual (schematics more importantly) for the EM101 its nice and easy. The filter chip is used almost identically to the SH101, feedback is just adding some of the output back inverted into the input. I added a new opamp into the EM101 for this. The frequency control is adding into the current summing node on pin 9 of the IR3109.

Wow, it must be a EM 101 sort of month because I just picked one up as well.

Reve, thanks so much for posting all of this information. It was incredibly helpful. Very nice explanations. Awesome stuff.

Although scans of the Service Manual would be amazing, I'd be happy with just a scan of the schematics. I could even put the file online myself if it exceeds the size limit at EM. I also have a lot of obscure scans that I've done that I could use as a bribe to motivate you

Definitely the same architecture and Osc section as in the Korg Poly-800. IT's using Rademacher synthesis, a subset of Walsh functions, so one other thing you could do is to re-create the missing Walsh harmonics and mix them back before the filter.

But yes, even on the Korg Poly-800 this ends up being a lot of work. I found it better to create two External Audio Input jacks which mix into the Filter at the line for each osc1.

The MSM chip also provides two solo Square/Rectangle pins 1, 2 as well as an always-on Noise output.

ohhh my mistake, I misread you to mean you'd added an ext audio-in to an EM-101. interesting reading nonetheless!

And I though you were asking about the Poly-800

In any case, since the architectures are similar, you might get some useful ideas from the Poly-800 mods too. The best is to get External Audio into the VCF and get some manual control over Cutoff Frequency & Resonance.

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